The goal of this pilot project is to determine whether positron emission tomography (PET) can demonstrate the location of cerebral regions of major functional significance (primary motor cortex and language cortex) in patients with brain tumors or vascular malformations. The subjects will be patients for whom tumor resection is planned or considered or in whom interstitial 125I brachytherapy is being considered. The PET results may be used to guide tumor resection or to help with the decision to perform tumor resection or brachytherapy.The brain regions associated with greatest risk of deficits following brain tumor resection or brachytherapy are primary motor cortex and primary language areas. Although the general location of these regions is well known anatomically, their location is somewhat variable in normals and may be altered in patients with brain tumors, and neurosurgeons have no satisfactory means of accurately localizing these regions at craniotomy.In this project, we study patients who have been demonstrated by CT or MRI to have a brain tumor close to primary motor or language cortex. In a single session, patients will undergo a series of PET scans with [15O]-H2O while awake and resting and during a series of stimulations including motor activation with finger tapping or foot tapping, sensory activation with a vibrator applied to the hand or foot, and language activation during a simple naming task. Statistical techniques will be applied to determine areas of significant activation in individual patients. Images showing the areas of activation will be provided to the neurosurgeons and other physicians involved in their care for potential use in patient management. We will determine the frequency with which activation can be demonstrated.